I'm not sure exactly what you're looking for in an answer here, whether you're trying to find out how long Vyvanase works for, or how long it takes it to completely leave your system, so I'll give you both.

Vyvanase claims that it is effective for up to 12 hours, the best information I was able to find was that the last of the vyvanase breaks down into Dextroamphetamine within 8 hours, which would make the 12 hour claim seem accurate.

As for the total time to clear your system after you stop taking it, information is scarce, but I was able to find a reference that 96.3% of all ingredients are excreted within 120 hours.